Considerable progress has been achieved in the last decade in the biochemical, molecular biological and structural analysis of ligand:protein interactions. Such interactions are the foundation stone for the operation of membrane protein systems, intra-cellular biochemistry and gene regulation. An understanding of the molecular details controlling ligand selectivity and binding would be a significant step forward. The tools of molecular dynamics computer calculations have already proven instrumental in analyzing the functional implications of globular protein tertiary structure and are being applied in understanding the free energy changes of binding in a wide range of systems. The lipocalin superfamily of hydrophobic binding proteins is an ideal system for analyzing in considerable detail the molecular factors involved in ligand recognition. This is because of the relatively small size (160 to 180 amino acids), diverse range of ligand selectivities, and the availability of five tertiary structures. The proposed research will utilize molecular dynamics calculations to analyze the molecular details of selectivity.